Sounds a bit barbaric but it probably works ok. An extractor has a high start up load so any dc drive you pick out should have a very long accel or better yet be able to run in "current limit" otherwise the motor armature will cook. The variac is an analog device which I have no problem with but it requires more "clap trap" to step it up (the accel). This will also cook the armature if done too quickly.It is a Variac, advanced by a timer motor, that trips a off delay relay, rectified by a bridge.
It is easy to fix, and most parts are generic.
Used these also but you need to order this one to get the 8 second accel. http://www.automationdirect.com/adc.../High_Voltage_(>_50V)_Enclosed/GSD4-240-10N4XYou did not mention the voltage of the motor, but this one would probably work: http://www.automationdirect.com/adc...s/High_Voltage_(>_50V)_Open_Frame/GSD4-240-5C
The price is right, and A-D is a great company to deal with.